With continuous shrinking of semiconductor process node dimensions, conventional lithography process, i.e., a patterning process that uses one photomask, has encountered limitation. That is, because the pitch between adjacent patterns is often too small, adhering between adjacent patterns can occur due to an optical proximity effect.
As the critical dimensions of semiconductor devices become smaller and smaller, a double patterning method has been used to solve the problem described above. With the double patterning method, a pattern to be formed is divided into two kinds of patterns, a first mask pattern and a second mask pattern. Next, a first pattern is formed using a first patterning process, and a second pattern is formed using a second patterning process. Thus, using such a double patterning method, the optical proximity effect caused by overly small pitch between adjacent patterns can be avoided.
Conventionally, a polysilicon layer can be patterned using a double patterning process, and then be etched to form a polysilicon gate, so as to improve accuracy and uniformity of the size of the polysilicon gate. A first mask pattern can be used in a first patterning process on the polysilicon layer to form a strip-shaped gate pattern. Further, a second mask pattern can be used in a second patterning process on the polysilicon layer to cut the strip-shaped gate pattern to form the polysilicon gates.
Typically, the second mask pattern has a relatively low pattern density and an uneven pattern distribution, which can cause a relatively significant lithography loading effect and a relatively small process window, and can eventually result in inaccurate size of exposed patterns during the second patterning process using the second mask pattern. Thus, during a subsequent etching process, the size of the polysilicon gates formed after cutting the gate pattern can have a relatively large deviation. The size of the formed polysilicon gates can thus be inaccurate. The disclosed methods and structures are directed to solve one or more problems set forth above and other problems.